Concentrations of free amino acids in blood plasma of rats force-fed l-glutamic acid, l-glutamine or l-alanine

Abstract

The concentrations of glutamic acid, glutamine, alanine, proline, threonine, glycine, valine, leucine-isoleucine, phenylalanine, and lysine were measured in the portal and systemic plasma of rats that had been forced-fed l-glutamic acid, l-glutamine, or l-alanine. The administration of glutamic acid resulted in a marked rise in the concentration of this amino acid in the portal plasma and a smaller one in the systemic plasma. It also caused the concentration of alanine to increase in the portal and to a lesser extent in the systemic plasma and the concentration of glutamine to increase substantially in both. Administration of glutamine (same molar quantity as for glutamic acid) resulted in greater increases in portal and systemic plasma concentrations of glutamine than were observed for glutamic acid after glutamic acid administration. It also caused the concentration of glutamic acid to increase in the portal and to a lesser extent in the systemic plasma, and the alanine concentration to increase markedly in both. Administration of alanine (1.6× the molar quantity used for glutamic acid or glutamine) resulted in a maximum increase in the portal plasma concentration of alanine which was 8× (on a molar basis) that observed for glutamic acid and 3× that observed for glutamine in the previous experiments. The systemic plasma alanine concentration also rose but much less than the portal concentration. The concentration of glutamic acid increased measurably in the portal plasma while the concentration of glutamine increased more in the systemic than in the portal plasma. The plasma concentrations of the other amino acids tested were not significantly altered in any of the experiments.